Larry Wayne Morris has written:

'Extraversion and introversion' -- subject(s): Extraversion, Introversion, Personality

The Minnesota Identical twins study indicates that much of what we call extraversion and introversion is an inherited preference. Of course, like all inherited traits, the environment can either promote or suppress development.

David B. Palmer has written:

'The extraversion-introversion dimension of personality and social conformity' -- subject(s): Personality

Both are correct.

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The term "extraversion" (and therefore "extravert") was first used (and possibly coined) by Carl Jung (along with "introversion") in 1913 but over the years the technically incorrect alternative spelling "extroversion" has become widely used.

Alex T. Quenk has written:

'Psychological types and psychotherapy' -- subject(s): Psychotherapist and patient, Extraversion, Typology (Psychology), Introversion

'Dream thinking' -- subject(s): Dream interpretation, Jungian psychology, Psychoanalysis, Dreams